1. Field of the Invention
The present invention relates to a multimedia broadcast/multicast service (MBMS), and particularly, to an apparatus and method for transmitting information for supporting mobility of a terminal and providing an MBMS.
2. Description of the Related Art
A universal mobile telecommunications system (UMTS) is a third generation mobile communications system that has evolved from a specification known as the European Global System for Mobile communications (GSM) system which aims to provide an improved mobile communications service based on a GSM core network and a wideband code division multiple access (W-CDMA) technology. FIG. 1 illustrates a network structure of a UMTS system to which the conventional art and the present invention are applied.
As illustrated in FIG. 1, the UMTS system is broadly comprised of a terminal, or user equipment (UE), a UTRAN 2 and a Core Network (CN) 3. The UTRAN 2 includes more than one Radio Network Sub-system (RNS) 4, each of which includes a single Radio Network Controller (RNC) 5 and more than one Node B 6 managed by the RNC. The RNC 5 manages the Node B 6, which serves as an access point of the UTRAN 2 for the terminal by receiving information transmitted from a physical layer of the terminal over an uplink and transmitting data to the terminal 1 over a downlink. The RNC 5 allocates and manages radio resources, and serves as an access point of the CN 3.
FIG. 2 illustrates a connection structure between the UTRAN 2 and the terminal 1 within the UMTS network. As illustrated in FIG. 2, the terminal 1 is connected with the CN 3 in order to receive services provided from the UMTS and information of the terminal and the CN is transmitted via the UTRAN 2.
The CN 3 is connected to the RNC 5 through an Iu interface in order to transmit and receive data and control messages. Each terminal 1 connected to the UMTS network is managed by a specific RNC 5 within the UTRAN 2. A Serving RNC (SRNC) 5 is the RNC for managing terminals. In other words, the SRNC 5 refers to the RNC that serves as the access point with the CN 3 for transmitting data to a specific terminal 1.
The SRNC 5 performs as a second layer of an Open System Interface (OSI) for data coming through a radio interface or being transmitted to the terminal and allocates radio resources appropriate to provide services. The function of managing radio resources performed by the SRNC 5 includes control functions associated with the specific terminal 1, such as setting transport channels, determining a handover and performing an Open Loop Power Control. The terminal 1 connected to the CN 3 through the UTRAN 2 at a specific time point has only one SRNC 5.
In general, one RNC 5 is used between the terminal 1 and the CN 3. However, if the terminal 1 moves to a new area managed by another RNC 5, the terminal is connected to the RNC at the new area via the RNC of the previous area.
For instance, it is assumed that the terminal is initially connected to the CN 3 through R1 (RNC1), but the terminal moves to an area or cell managed by R2 (RNC2). After moving to the area managed by R2, the terminal 1 is connected to R1 through an Iur interface via R2. R1 manages the terminal and serves as an access point with the CN 3 and R2 partially performs functions of routing user data or allocating codes, specifically, common resources. In the UMTS network, every RNC 5 connected to the terminal 1, such as R2, other than the SRNC is referred to as a Drift RNC (DRNC). Therefore, one terminal 1 may have no DRNC 5 or may have one or several DRNCs according to its connection state.
The SRNC 5 and the DRNC are logically divided with relation to a specific terminal 1 . However, the RNC 5 and the Node B 6 within the UTRAN 2 have a subordinate relation there between and, accordingly, the RNC can be divided at the side of the Node B. In order to distinguish between the RNC 5 managing the Node B 6 and other RNCs, an RNC managing a specific Node B is referred to as a Controlling RNC (CRNC). Specifically, the RNC 5 that is connected to a specific Node B 6 via an Iub and controls radio resources of the Node B corresponds to the CRNC of the specific Node B and there is a one-to-many relation between the CRNC and the Node B in the structure of the UTRAN 2. The CRNC 5 performs functions such as load control and congestion control of traffic within a cell that the CRNC manages, acceptance control for a new radio link set within this cell and code allocation.
A Radio Resource Control (RRC) layer is defined at a third layer of a radio protocol located in the RNC 5 and the terminal 1. The RRC handles the controlling of transport channels and physical channels related to establishment, reconfiguration, and release of Radio Bearers (RBs). An RB denotes the services provided by a second layer of the radio protocol for data transmissions between the terminal 1 and the RNC 5. In general, establishing the RB denotes the processes of stipulating the characteristics of a protocol layer and a channel, which are required for providing a specific service, and setting the respective detailed parameters and operation methods thereof.
The RRC state refers to whether the RRC of the terminal 1 is logically connected to the RRC of the UTRAN 2, thereby forming a logical connection with the RRC of the UTRAN. If the RRC of the terminal 1 forms a logical connection with the RRC of the UTRAN 2, this is referred to as an RRC connected state. Conversely, if there is no logical connection between the RRC of the terminal 1 and the RRC of the UTRAN 2, this is referred to as an RRC idle state.
When the terminal 1 is in the RRC connected state and, accordingly, the UTRAN 2 can recognize the existence of the corresponding terminal according to units of cells, the UTRAN can effectively control the terminal. On the other hand, the UTRAN 2 cannot recognize a terminal 1 that is in idle state. The terminal 1 in idle state can be managed by the CN 3 according to units of location areas or units of routing areas, which are areas larger than the cell. Specifically, the existence of a terminal 1 in idle state is only recognized according to units of large areas, such as location areas or routing areas, and the terminal must transition into the connected state in order to receive typical mobile communication services such as voice or data.
FIG. 3 illustrates an RRC state transition of a terminal 1. As illustrated in FIG. 3, when a user turns on the power of the terminal 1, the terminal first detects an appropriate cell and maintains its idle state in the corresponding cell. The terminal 1 in idle state forms an RRC connection with the RRC of the UTRAN 2 through the RRC connection procedure and transitions into the RRC connected state when the RRC connection needs to be formed.
There are several instances in which a terminal 1 in idle state is required to form the RRC connection. For example, an uplink data transmission may be required due to a call attempt by a user or the transmission of a response message in response to a paging message received from the UTRAN 2 may be required.
A Multimedia Broadcast/Multicast Service (MBMS) refers to a service for providing streaming or background services to a plurality of terminals 1 using a downlink dedicated MBMS bearer service. In the UTRAN 2, the MBMS bearer uses a point-to-multipoint radio bearer (RB) and a point-to-point RB.
The MBMS is divided into a broadcast mode and a multicast mode. The MBMS broadcast mode is a service for transmitting multimedia data to all users within a broadcast area. The broadcast area refers to a region where the broadcast service is possible. Conversely, the MBMS multicast mode is a service for transmitting the multimedia data only to a specific user group within a multicast area. The multicast area refers to a region where the multicast service is possible. The multimedia area and broadcast area are referred to as a service area.
FIG. 4 illustrates a conventional procedure for providing a specific MBMS (service 1) from a UMTS network to a terminal (UE) 1 by using a multicast mode. A UE 1 that desires to receive an MBMS subscribes to the service, a process referred to as subscription. Subscribing refers to establishing a relationship between a service provider and a user.
Terminals 1 desiring to receive the MBMS should receive a service announcement provided by the network 3. The service announcement refers to providing to the terminal 1 an index and any related information of the services to be provided. Specifically, a terminal 1 desiring to receive the MBMS of the multicast mode should join a multicast group. The multicast group refers to a group of terminals 1 receiving a specific multicast service and joining refers to one user merging with the other users in a multicast group to receive the particular multicast service.
The terminal 1 can inform the UMTS network that it desires to receive specific multicast data through MBMS multicast joining. Conversely, a procedure whereby a terminal 1, having joined a specific multicast group, is no longer a part of the multicast group is referred to as leaving. Each terminal 1 performs the subscribing, joining and leaving processes. The terminal 1 can perform the subscribing, joining, and leaving processes at various times, such as before data transmission, during the transmission, or after the transmission.
While a specific MBMS is ongoing, one or more sessions can sequentially be generated with respect to the corresponding service. If data to be transmitted for the specific MBMS is generated in an MBMS source, the CN 3 notifies the RNC 5 of the start of a session. Conversely, when there is no more data to be transmitted for the specific MBMS in the MBMS source, the CN 3 notifies the RNC 5 of a session stop. The data transmission with respect to the specific MBMS can be carried out between the session starting and the session stop. The data transmitted through the data transmission process can be transmitted only to the terminals 1 having joined the multicast group for the specific MBMS.
In the session starting process, the RNC 5, having received the session starting from the CN 3, transfers an MBMS notification to the terminals. The MBMS notification refers to the RNC 5 informing a terminal 1 that the data transmission of the specific MBMS in a cell draws near or is impending. The MBMS notification is transmitted more than one time before actual data of the service is transmitted. The RNC 5 may also count the number of terminals receiving the specific MBMS within one specific cell using the MBMS notification process. The counting procedure is used for determining whether a point-to-multipoint RB or a point-to-point RB should be set as the RB for transmitting the specific MBMS, or whether no RB should be set.
The RNC 5 internally establishes a threshold value to select an appropriate MBMS RB. After the RNC 5 counts the number of terminals 1, if the counted number of terminals existing within the corresponding cell is smaller than the threshold value, the RNC establishes a point-to-point RB, while a point-to-multipoint RB is established if the counted number of terminals is greater than the threshold value. After determining the MBMS RB, the RNC 5 informs the terminals 1 of the establishment information of the corresponding RB.
When the point-to-point RB is established for the specific service, the terminals 1 desiring to receive the service are all in the RRC connected state. However, when the point-to-multipoint RB is established for the specific service, all terminals 1 desiring to receive the service do not have to be in the RRC connected state. That is, terminals 1 in an idle state can also receive the MBMS data by using the point-to-multipoint RB. When MBMS data is transmitted from the CN 3 during one session of the MBMS, the RNC 5 initiates data transmission using the established RB, and releases the pre-established RB when the CN transmits a session stopping message.
However, if there is no terminal 1 that desires to receive the specific MBMS, the RNC 5 does not establish any RB and does not transmit the MBMS data. Establishing an RB by the RNC 5 even if there is no user who wants to receive the service would cause undesirable consumption of radio resources.
The MBMS area refers to an area configured with cells supporting MBMSs to which a specific terminal 1 has subscribed. The MBMS area is constructed by combining more than one cell, and may be constructed with cells managed by one RNC 5 or be located over areas managed by several RNCs. A list of neighboring cell information refers to a list including information of cells managed by the DRNC 5 that is positioned adjacent to the RNC.
FIG. 5 illustrates an MBMS attaching procedure. As illustrated in FIG. 5, the RNC 5 providing an MBMS recognizes and manages a terminal 1 in the RRC connected state among terminals having joined a specific MBMS for every cell that the RNC manages. The RNC 5 makes a list, such as an RRC connected terminal list, of terminals 1 in the RRC connected state for each MBMS of each cell. The RRC connected terminal list includes identifiers, such as URNTI, of the terminals 1 having joined the specific MBMS.
As part of the MBMS attaching procedure, when the terminal 1 has moved from a cell managed by the SRNC 5 into a cell managed by the DRNC, the SRNC receives a session start message from the CN 3 with respect to an MBMS that a terminal in the RRC connected state has joined, both for those services that are ongoing and those services that are not ongoing. Thereafter, the SRNC 5 transmits terminal information to the DRNC through an MBMS connection or attachment request message, such that the DRNC adds terminals 1 which request the MBMS connection to the RRC connected terminal list that the DRNC manages. The MBMS connection request message includes an ID of a cell to which the terminal 1 has moved, IDs of any MBMS that the terminal is joining and the URNTI of the terminal.
Once the MBMS connection or attachment request message for a specific terminal 1 is received from the SRNC 5, if it is possible to allocate resources for maintaining the RRC connected state with respect to the corresponding terminal. The DRNC 5 grants the MBMS connection request of the terminal 1. The DRNC 5 then adds the URNTI of the terminal 1 to the RRC connected terminal list for each MBMS that the moved terminal has joined.
The DRNC 5 then transmits a positive response to the SRNC through an MBMS connection response message. The SRNC 5, having received the message, maintains the terminal 1 in the RRC connected state even in the new cell. The SRNC 5 also transmits the MBMS data to the terminal 1 using a point-to-point RB. Specifically, the MBMS data is transmitted to the DRNC 5 through the SRNC and then transmitted to the terminal 1 through the DRNC using the point-to-point RB.
The DRNC 5 does not always grant the MBMS connection request upon receiving the MBMS connection request message for the specific terminal 1 from the SRNC. If the DRNC 5 forms the RRC connection for the terminal 1 but there are no resources for maintaining the terminal in the RRC connected state, the DRNC denies the MBMS connection request of the terminal and transmits a negative response to the SRNC.
However, in the conventional art, if a terminal 1 located outside each MBMS area is connected to the DRNC 5, problems may occur. When the terminal 1 has moved to the MBMS area managed by the DRNC 5 that provides an MBMS to which the terminal has subscribed, the moved terminal obtains information of the corresponding service by receiving a notification from the DRNC or receives information of the MBMS through a MBMS Control Channel (MCCH).
At this time, the MBMS can be transmitted using a point-to-point RB or a point-to-multipoint RB. When the DRNC 5 provides the MBMS using the point-to-point RB, the terminal 1 should receive the MBMS directly from the SRNC instead of from the SRNC via the DRNC by setting a dedicated channel. However, it is impossible for the SRNC 5 to accurately recognize whether the DRNC is providing the MBMSs to which the terminal 1 has subscribed or that the MBMSs are being provided using the point-to-point RB.
Accordingly, the SRNC 5 cannot set the dedicated channel for the terminal 1 to receive the MBMS using the point-to-point RB and, therefore, the terminal cannot receive the MBMS. Specifically, when a terminal 1 has moved from an area managed by the SRNC 5 to an area managed by DRNC and has been connected to the DRNC, even though the MBMS to which the terminal has subscribed is being transmitted through the point-to-point RB via the DRNC, the SRNC can not accurately recognize the state of the MBMS in the DRNC and the SRNC cannot set the dedicated channel with the terminal. As a result, the terminal 1 cannot receive the MBMS.
Therefore, there is a need for an apparatus and method for transmitting information for supporting mobility of a terminal and providing an MBMS. The present invention addresses these and other needs.